645D + 45mm 6X7 with Pentax 645-67 adaptor

It might be worth approaching it from the other direction too... seek out a dealer in Japan who *does* ship outside Japan and see if he can get the P645 lenses, if only on a special order basis. I'm thinking first of:
Noriaki Hishinuma
Matsuiya International Corp
1-49-2, Higashiuragacyo, Yokosuka,
Kanagawa, Japan 2390821
Phone 81-90-2168-0867 Matsuiyastore items - Get great deals on AF, MF items on eBay Stores!
eBay: matsuiyastore
email: ford4830@yahoo.co.jp

I've found the 45-85mm manual lens to be very sharp right into the corners at 45 and 65 on the 645D, with just a trace of fixable corner softening and CA at 85. Haven't tried any other 45mm alternative.

All Pentax 645 lenses should benefit from the "sweet-spot" effect since they were designed to cover an image frame of at least 56-42mm - much bigger than the 44x33 of the 645D.

Pentax didn't do use any favors by identifying the difference between the later lens generations as 6x7 and 67 but saying something like SMC Pentax 6x7 55mm and SMC Pentax 67 55mm clearly identifies which generation of the 55mm your talking about, for example, and that is the markings you'll see on the lens in addition to the cosmetic differences.

Tuco, you're right. My misinterpretation was caused by some ads which had the wrong photo of lenses, so that I was led to believe there were actually two 67 versions. I now know that there's only one!